Tehri Dam, one of India's highest dams, is constructed on which of the following rivers?

Introduction / Context:
This question relates to Indian rivers and major dam projects, an important area in geography and general awareness. Tehri Dam is a well-known multi-purpose project in Uttarakhand, frequently mentioned in discussions on hydropower, displacement and environmental issues. Many learners confuse whether it is on the Ganga itself or on one of its upper tributaries.

Given Data / Assumptions:
- The dam specified is Tehri Dam, located in Uttarakhand.
- The options list several major rivers: Brahmaputra, Godavari, Ganga, Bhagirathi and Alaknanda.
- The task is to identify the specific river on which the dam structure is built.
- We assume the standard hydrological definition of the river at the dam site.

Concept / Approach:
In the upper Himalayas, the Ganga is not yet formed as a single river. Instead, its main headstreams are the Bhagirathi and the Alaknanda, which meet at Devprayag to form the Ganga. Tehri Dam is constructed at a site where the river is still known as the Bhagirathi. Therefore, although Tehri is part of the larger Ganga system, the exact river on which the dam stands is Bhagirathi, not the already-formed Ganga or the Alaknanda.

Step-by-Step Solution:
Step 1: Recall that Tehri Dam is a major hydropower and irrigation project in the Garhwal region of Uttarakhand.Step 2: Understand that the Ganga in its upper course has two main headstreams: Bhagirathi and Alaknanda.Step 3: Note that these two rivers meet at Devprayag, and only after this confluence is the river officially called Ganga.Step 4: Tehri town and the dam site are located upstream of Devprayag on the Bhagirathi River.Step 5: Therefore, the concrete dam structure is across Bhagirathi, not directly across the river named Ganga or across Alaknanda.

Verification / Alternative check:
You can verify this by looking at a detailed map of Uttarakhand, following the course of Bhagirathi from Gangotri downwards. Tehri lies along this course before Bhagirathi meets Alaknanda at Devprayag. Government project descriptions and standard exam guides consistently state that Tehri Dam is on the Bhagirathi River, though they may also describe it as part of the Ganga basin. This confirms Bhagirathi as the correct answer.

Why Other Options Are Wrong:
Brahmaputra: A major river of northeastern India, Tibet and Bangladesh, far away from Tehri in Uttarakhand.
Godavari: A peninsular river flowing mainly through central and southern India; not related to Tehri Dam.

Ganga: The dam is located upstream of the confluence where the river is still called Bhagirathi, not yet named Ganga.
Alaknanda: Another major headstream, but Tehri Dam is not built on its course; it lies on Bhagirathi.

Common Pitfalls:
The most common error is selecting Ganga because many textbooks loosely describe Tehri as a project on the Ganga system. Another confusion occurs between Bhagirathi and Alaknanda because both are headwaters of the Ganga and are often mentioned together. To avoid mistakes, remember that the official point where Ganga begins is Devprayag, and Tehri is located upstream on Bhagirathi before this confluence.

Final Answer:
Bhagirathi